ABSTRACT
1. The Bartha K and NIA-4 strains of Aujeszky's disease virus (ADV) were non-pathogenic for rabbits vaccinated once or twice by nasal instillation or intramuscular injection. Neutralizing antibodies were detected in 68% of the rabbits two weeks after primary vaccination and in al rabbits at challenge. 2. Challenge doses of virulent ADV greater than 10**5.0 median tissue culture infective doses (TCID50) resulted in the death of most vaccinated and all unvaccinated rabbits with typical signs of Aujeszky's disease withing 4 days. ADV was recovered from braim and lung suspensions of vaccinated and unvaccinated rabbits who had died as a result of the challenge. 3. When the challenge dose was reduced to approximately 10**3.0 TCID50, rabbits vaccinated twice survived while al unvaccinated controls died within 3 days